1. Field of the Invention
The present invention relates to an organic electroluminescence display device.
2. Description of the Related Art
Organic electroluminescence display devices (organic EL display devices) are self-light emitting type display devices and are for use in display and illumination. The organic EL display has such advantages of display performance that it is high in visibility, and free from viewing angle dependency, as compared to conventional CRTs and LCDs, and also has advantages in that display devices can be made lighter and thinner. Meanwhile, organic EL illumination has advantages, in addition to enabling lighter and thinner devices, in possibility of achieving lighting fixture having a shape that has not yet been achieved so far, by using a flexible substrate.
The organic electroluminescence display devices have superior features as described above, but the refractive index of each of layers constituting a display device, including a light emitting layer, is higher than the refractive index of air. For instance, in an organic electroluminescence display device, an organic thin-film layer, such as a light emitting layer, has a refractive index of 1.6 to 2.1. Therefore, emitting light is liable to be totally reflected at an interface, and the efficiency of extraction of light is less than 20%. Thus, the majority of light is lost.
As measures for improving the efficiency of extraction of light, for example, the following methods are proposed: a method in which a transparent layer is provided adjacent to a transparent electrode on a light extraction surface side, and an area for substantively causing reflection of light and disturbance of scattering angle adjacent to the light extraction surface of the transparent layer or inside the transparent layer (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2004-296429); a method in which in an optical path in which light emitted from a light emitting layer travels from an organic substance layer to a light transmissive insulating layer, a fine particle-dispersed layer is provided, in which fine particles are dispersed in a base material (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2006-107744); a method of forming a diffraction grating or a zone plate at a position where total reflection at an interface of an organic EL element is prevented (for example, see Japanese Patent (JP-B) No. 2991183); and a method in which an optical unit is provided, between a light transmissive substrate and a light transmissive electrode, which is configured so that, in a range of angles at which light is totally reflected at an interface between the light transmissive substrate and the light transmissive electrode, at least a part of light incident on the light transmissive electrode is scattered and/or diffracted to go out via the light transmissive substrate, and incident light entering the light transmissive substrate and the light transmissive electrode is weakly scattered and/or transmitted to go out via the light transmissive substrate (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2006-54197).
However, in the method disclosed in JP-A No. 2004-296429, in order to improve the efficiency of light scattering, it is necessary to thicken the thickness of the area for causing reflection of light and disturbance of scattering angle, and thus it is difficult to make a hole in the area, making it impossible to use the method in organic electroluminescence display devices.
In the method disclosed in JP-A No. 2006-107744, the fine particle-dispersed layer has a thin thickness and fine particles contained therein have large diameters, and thus leading to poor light scattering efficiency, and the fine particles easily aggregate, leading to large-size concaves/convexes in a surface of the fine particle-dispersed layer, resulting in occurrence of image bleeding and image blur. Furthermore, the method disclosed in JP-A No. 2006-107744 has a problem that the production process is complex.
The methods disclosed in JP-B No. 2991183 and JP-A No. 2006-54197 cause a problem that the efficiency of extraction of light is still insufficient.